I'm wicked dumb, so I don't know how to activate a foundry quest. Only accepted a few. /smackshead
A bunch of ways.
Hit K. to the right, you can open the foundry menu.
Use a posterboard, in any bar, in the main marketplace, or at the start of most zones.
Talk to a Harper agent. This has the advantage of listing"local" ones first. So, if you are in the tower district, foundry quests that occur in the tower district will be listed first.
then the quest marker should tell you a place to go or person to talk to. Many have you use the city gates, to travel to unique locations.
Foundry quests scale with your level. the only problem with this is, they might send you to locations in high level zones that don't scale.
One of the top rated, in the menu right now is "the hidden blade". that one starts in the town center, so all levels can do it. you can do it right out of the level 3 intro.
It sends you to a door right next to the marketplace. (right next to the lost jewels quest)
however the followup quest by the same author, sends you to the tower district. Although, you CAN get to the npc safely with no combat. just hug left.